1. Field of the Invention
This invention relates to pressure sensors that sense a fluid pressure such as a air pressure and more particularly to a pressure sensor that utilizes an extension type conductive elastomer that, when extended, will change its electrical resistance value in response to an extension thereof, and thereby in response to the magnitude of the extending force as well.
2. Prior Art
A pressure sensor that utilizes a pressure sensitive conductive rubber (PCR) in its construction is well known. Such pressure sensitive conductive rubber, as heretofore in use however, while it changes its electrical resistance when compressed, will rupture when a tensile force is applied thereto. Therefore, it should be used in such a manner that it will be compressed to sense a pressure, but never extended. However, generally, an elastomer such as a rubber, will have elasticity modules in compression that is considerably larger than it exhibits in tension, and this means that a smaller compressive force cannot cause a deformation to a significant extent in an elastomer. Accordingly, the conventional pressure sensor utilizing a pressure sensitive conductive rubber cannot be utilized for sensing a fluid pressure such as air pressure. On the same account, in an elastomer, practically, a large deformation cannot be caused by compression, as an extremely great force is required to cause it. Therefore, the conventional pressure sensor utilizing a pressure sensitive conductive rubber is limited to sensing a pressure through a change of its electrical resistance for a very small compressive deformation only. This limitation makes it impractical for use in sensing a pressure where a high degree of accuracy is required. Additionally, pressure sensitive rubber exhibits large hysteresis as a result of application of a compressive force thereto, further prohibiting accurate sensing.
As a consequence, pressure sensitive conductive rubbers have heretofore been limited in application to devices, such as a switching device, that sense a pressure applied thereto through a solid substance or semi-solid substance such as a finger or foot of a human body and that sense the presence or absence of pressure in an on/off fashion only, and cannot sense an applied pressure in an analog fashion as does the present invention.